13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- The electric current was applied to heal the fatigue crack. The application of electric current was carried out using a transistor type power source. The pulse current was applied through the electrodes striding across the notch as shown in Fig. 3. The chromium cupper electrodes of 5 mm in diameter were used. Two electrodes were connected straddling the notch of the specimen. The distance between two electrodes was 1.3 mm. The conditions of the application of the electric current are shown in Table 4. The pulse electric current was applied to the specimen once and more, and the crack state on the specimen surface was observed with a scanning electron microscope (SEM) before and after every application of the electric current. Table 1. Chemical compositions of the stainless steel SUS316 (wt. %) C Si Mn P S Ni Cr Mo Fe 0.05 0.26 1.3 0.028 0.03 10.1 17.09 2.01 Balance Table 2. Mechanical properties of SUS316 Yield stress Tensile strength Young’s modulus Poisson’s ratio Hardness [MPa] [MPa] [GPa] HBW 300 573 193 0.3 161 Specimen A Specimen B Standard The maximum gross stress σmax [MPa] 180 150 150 Stress ratio R 0.05 0.05 0.05 Frequency f [Hz] 10 10 10 Pre-crack length a [mm] 1.55 1.08 - Table 4. Conditions of the electric current Specimen A Specimen B Applied current [A] 4000 8000 Pulse duration [msec] 2.0 1.0 The Number of current application 12 1 Figure 1. Schematic of specimen t = 2.5 4-R20 25 15 140 45 72 Table 3. Fatigue test and crack conditions before current application Notch length : 2.0 mm Root radius of notch : 0.2 mm
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